This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-286438 filed in Japan on Nov. 7, 2008, the entire contents of which are herein incorporated by reference.
The present invention relates to a vehicle control apparatus equipped with an engine (internal combustion engine), a torque converter, and an automatic transmission.
In a vehicle equipped with an engine, as a transmission that appropriately transmits torque and revolution speed generated by the engine to drive wheels according to the running state of the vehicle, an automatic transmission is known that automatically optimally sets a gear ratio between the engine and the drive wheels.
Examples of an automatic transmission mounted in a vehicle include a planetary gear transmission that sets a gear using frictionally engaging elements such as a clutch and a brake and a planetary gear apparatus, and a belt-driven stepless transmission (CVT: Continuously Variable Transmission) that steplessly adjusts the gear ratio.
In a vehicle in which a planetary gear-type automatic transmission is mounted, a gearshift map that has gearshift lines (gear switching lines) for obtaining an optimal gear according to the vehicle speed and an accelerator opening degree (or throttle opening degree) is stored in an ECU (Electronic Control Unit) or the like, a target gear is calculated with reference to the gearshift map based on the vehicle speed and the accelerator opening degree, and based on that target gear, a gear (gear ratio) is automatically set by engaging or releasing a clutch, a brake, a one-way clutch, and the like, which are frictionally engaging elements, in a predetermined state.
In the configuration of a belt-driven stepless transmission, a belt is wrapped around a primary pulley (input side pulley) and a secondary pulley (output side pulley) that are provided with a pulley groove (V groove), and by reducing the groove width of one pulley while increasing the groove width of the other pulley, the contact radius (effective diameter) of the belt to each of the pulleys is continuously changed to steplessly set a gear ratio.
In a vehicle equipped with such an automatic transmission, a torque converter is disposed in a power transmission path from the engine to the automatic transmission. The torque converter, for example, is provided with a pump impeller connected to an engine output shaft (crank shaft), a turbine runner connected to an input shaft of the automatic transmission, and a stator provided between the pump impeller and the turbine runner via a one-way clutch. The torque converter is a hydraulic transmission apparatus in which the pump impeller rotates according to rotation of the engine output shaft, and the turbine runner is rotationally driven by operating oil discharged from the pump impeller, thus transmitting engine output torque to the input shaft of the automatic transmission.
Widely adopted is a torque converter provided with a lockup clutch that puts an input side (pump side) and an output side (turbine side) in a directly connected state, and by engaging (lockup on) or releasing (lockup off) the lockup clutch according to the operating state, the fuel consumption ratio (below, referred to as fuel consumption) is improved.
Also, in a vehicle equipped with this type of automatic transmission, a shift lever operated by a driver (user) is provided, and by operating the shift lever, it is possible to switch between, for example, a P position (parking range), an R position (reverse range), an N position (neutral range), a D position (drive range), and so forth. Also, recently, an automatic transmission whereby it is possible to select a manual gearshift mode has also come into use, and with such an automatic transmission, it is also possible to arbitrarily switch the gear ratio (gear) of the automatic transmission by operation of the shift lever by the driver (for example, see JP 2008-261440A and JP 2007-139059A).
In an automatic transmission in which a manual gearshift mode is selectable, a downshift allowable vehicle speed is set in order to prevent over-revving (over-revolutions) of the engine when downshifting in the manual gearshift mode, and downshifting of the automatic transmission is allowed in a circumstance in which the vehicle speed when there is a downshift request is less than the downshift allowable vehicle speed (for example, see JP 2001-336627A).
Also, in an automatic transmission in which a manual gearshift mode is selectable, when the manual gearshift mode is selected, engine over-revving is prevented by executing an automatic upshift that reduces the gear ratio of the automatic transmission in a circumstance in which the engine revolutions have reached a maximum allowable revolutions (for example, see JP 2007-139124A). Below, this control is also referred to as “automatic upshift control in manual gearshift mode”.
Technology for preventing engine over-revving in an automatic transmission in which a manual gearshift mode is selectable is also described in JP H10-89466A. In the technology described in JP H10-89466A, in the manual gearshift mode, downshifting is prohibited if engine revolutions when there is a downshift request exceed over-revolutions (maximum revolutions), and downshifting is allowed in a circumstance in which engine revolutions are no more than over-revolutions.
Incidentally, in a vehicle in which a manual gearshift mode is selectable, the downshift allowable vehicle speed is uniformly set. Moreover, because the engine revolutions fluctuate due to changes in vehicle state or the like, the downshift allowable vehicle speed is set to a low speed, allowing for a margin (degree of safety), such that engine over-revving can be prevented in all circumstances, even including such fluctuation. Therefore, there may be instances in which a downshift allowable region (region where a manual gearshift is possible in the manual gearshift mode) becomes small, and vehicle operability is reduced. Also, in automatic upshift control in the manual gearshift mode as well, for same reasons, the maximum allowable revolutions relative to engine revolutions are set low, and in this case as well, the region where a manual gearshift is possible in the manual gearshift mode is restricted.
The present invention was made in view of such circumstances, and it is an object thereof to provide a vehicle control apparatus whereby while preventing engine over-revving, it is possible to expand the region where a manual gearshift is possible in a manual gearshift mode.